What smart dogs mean by a dog door

What exactly does a dog door do? The cute big dog in this video also wonders when he comes from playing and just uses it for people - with nasty consequences for his owner!

If the dog can already decide when to go indoors and when not, it can also decide who stays outside, right? In this case it is his master.

Or did the four-legged friend just want to be good and close the door behind it so that it doesn't pull? You don't know, but it's always funny!

Cross-country with the dog: off through the middle!